SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
Two high frequency output clocks are available from APLL_PCIE. The direct output CLKVCOLDO supplies 2.5 GHz high speed transmision clock for the PCIe PHY RX module and the divided by 2 clock output CLKVCOLDO_DIV supplies high speed transmision clock (1.25 or 2.5 GHz) for the PCIe PHY TX module. The internal parameters of APLL (multipliers, dividers) are fixed and do not need programming to generate the output clocks. The output clock CLKVCOLDO_DIV is by default the divided by 2 version of the CLKVCOLDO. The divider is controlled by the RATE signal from the PCIe_SS controller. The by-2-divider has a bypass feature to ignore the division control from PCIe_SS and to output a clock with same frequency like CLKVCOLDO. This bypass feature is controlled by PRCM.CM_CLKMODE_APLL_PCIE[8] CLKDIV_BYPASS bit as follows:
The frequency of CLKVCOLDO_DIV can be changed on-the-fly, but glitches can occur on the clock. Best approach is to disable the CLKVCOLDO_DIV when changing the frequency. See Section 26.4.4.4.2.4.2.1 PCIe PHY APLL Output Clock Gating for CLKVCOLDO_DIV gating options.
The availability of the APLL_PCIE output clocks can be monitored in PRCM.CM_CLKVCOLDO_APLL_PCIE register as follows: